The present invention relates to an electromagnetic device for starting a plunger by magnetic flux generated by an electromagnetic coil.
Japanese Patent Application Publications Nos. H05(1993)-55029 and 2002-8498 disclose examples of existing bidirectional electromagnetic devices. A bidirectional electromagnetic device of one of these examples includes a magnetic path, two exciting coils and a plunger surrounded by the magnetic path. The magnetic path includes a first magnetic path part, a second magnetic path part, a leg part, central magnetic path parts, and an intermediate magnetic path part. The leg part connects the first magnetic path part and the second magnetic path part. The intermediate magnetic path part projects radially inward from an intermediate part of the tubular leg part. The central magnetic path parts each extend inwardly in parallel with the leg part from central parts of the first magnetic path part and the second magnetic path part substantially halfway to the intermediate magnetic path part. The two exciting coils are disposed in the thus-structured magnetic path. The plunger is attracted to or detached from the central magnetic path parts by electromagnetic forces of the exciting coils.
In this example, when one of the exciting coils is supplied with exciting current, the plunger is actuated upward by a magnetomotive force from the first magnetic path part, and is attracted to the upper central magnetic path part. Then, when the supply of the exciting current to the one of the exciting coils is stopped, and the other of the exciting coils is supplied with exciting current, the plunger is actuated downward by a magnetomotive force from the second magnetic path part, and is attracted to the lower central magnetic path part.
For the actuation of the bidirectional electromagnetic device of this example, the magnitude of the magnetomotive force, which is a product of the winding number of each of the exciting coils and the supplied current, is so determined as to correspond to a force required to be generated for starting the plunger; and the shape and size of the plunger, the magnetic path and other elements are so determined as to prevent a saturation of magnetic flux generated by the magnetomotive force.